Prenatal androgen organizes brain development and affects behavioral sex differences, perhaps including sex differences in spatial ability. This study investigates spatial cognition in rhesus monkeys, including males, females, and individuals who received testosterone, an androgen antagonist, or vehicle prenatally. The prenatal perturbations are relatively small and most often did not alter genital appearance, but have produced a suite of behavioral and neuroendocrine effects. Thus, the treatments mimic effects that might occur naturally in humans but remain undetected. During testing, subjects will navigate to locate food while their location in space is recorded by video tracking. Landmark presence and the spatial consistency of the food will be manipulated to permit analysis of strategy use. Circulating hormones will be monitored for evidence of an interaction between organizational and activational hormone effects. Also, the size of the hippocampus, the brain area most associated with spatial cognition will be measured with structural MRI. This study is the first experimental investigation of prenatal testosterone effects on hippocampal size and spatial abilities in nonhuman primates or humans, and the use of these treatments should further understanding of how prenatal hormone exposure may affect the adult brain and cognition.